Glass repair method

ABSTRACT

A method of repairing a crack in a windshield where the crack has a surfaced portion repair resin of a first viscosity is applied to the crack and then a second higher viscosity repair resin is applied over the same portion of the crack. In an alternative method where the crack has an unsurfaced or tight portion, two injectors are used to fill that portion with a lower viscosity resin.

REFERENCE TO RELATED APPLICATIONS

This patent is a continuation of patent application Ser. No. 08/155,452filed Nov. 19, 1993 now U.S. Pat. No. 5,425,827 which is acontinuation-in-part of patent application Ser. No. 07/881,625 filed onMay 12, 1992 now U.S. Pat. No. 5,429,692 which is a continuation-in-partof application Ser. No. 07/580,075 filed Sep. 10, 1990 now U.S. Pat. No.5,116,441 issued on May 12, 1992. The disclosures of the priorapplications and patents are hereby incorporated by reference in theirentirety into this application.

TECHNICAL FIELD

The present invention pertains to glass crack repair, and moreparticularly, to repair, in place, of automobile windshield cracks.

BACKGROUND ART

Various resin products are commercially available in the trade for therepair of glass cracks and, in particular, the repair of automobilewindshield cracks. Such repair may be done in place without removal ofthe windshield and saves the cost of windshield replacement. Thepracticality of an acceptable glass crack repair is principally due tothe fact that the index of refraction of the resin is substantially thesame as that of the glass.

A crack in glass is visible because as light rays pass the boundarybetween the glass and the air in the crack they are bent due to thedifference in the speed of light in glass as compared with the speed inair. Light that is reflected back from such boundaries comes at adifferent angle than if there were no crack and hence the eyes and brainof the observer sense the discontinuity. Index of refraction for anymaterial is a ratio of the speed of light in that material compared tothe speed in a vacuum. If two materials have the same index ofrefraction there will be no bending of the light rays at a boundarybetween the materials and an observer will not sense the discontinuity.Thus a crack filled with such a resin will essentially seem todisappear.

There are different formulations of resins. Some are aerobic or "airdrying" and others are cured or hardened by radiating them withultraviolet light which is usually provided by a lamp made for thispurpose. The aerobic resins come in two parts and are mixed before use.Their curing begins from the time of mixing whereas the cure of theultraviolet types begins when they are subjected to the ultravioletlight.

Automobile windshields are typically made of a "sandwich" of two layersof glass laminated to an inner layer of resin material such aspolybutyral. The windshield has a periphery which defines a glass areawithin the periphery for each glass layer. The glass area for each layerhas an exposed surface and an inner surface in contact with the innerplastic (polybutyral) layer. Also, for each glass layer there is an edgedefined by the periphery extending between the outer surface and theinner surface joining these surfaces at an angle such as 90° to form acorner. Many types of breaks may occur in such windshields. One, whichis usually caused by the impact of a rock, is called a "bullseye". Abullseye is a type of a stone break which has a circular appearance. Itoften has a cone shaped piece of glass detached from the outer layer.The apex of the cone faces the outer surface and the base of the conemay be forced partly into the inner layer. The apex may or may notconnect to the outer atmosphere.

Sometimes the impact of a rock or other object will result in smallradiating cracks from the impact point and is then called a "starbreak". A combination of a bullseye and a star, called a "combinationbreak", can also occur. Impacts often cause linear cracks inwindshields. They may originate at a stone break or may, instead,originate at a point. They may extend to the glass edge or they mayterminate at another point.

Various tools have been proposed to aid in filling stone breaks withresin. One is described in U.S. Pat. No. 3,993,520 to Werner andutilizes an injector assembly having a piston inside a cylinder. Whenthe piston is depressed the resin is injected out the open end of thecylinder and into the stone break. The assembly is held to the surfaceof the glass by suction cups.

A similar apparatus with an adjustable arm is disclosed in U.S. Pat. No.4,291,866 to Petersen. A variation of the Werner apparatus is in U.S.Pat. No. 4,569,808 to Small while U.S. Pat. No. 4,744,841 to Thomasutilizes vibration and heat. An apparatus with a spring loaded air exitis disclosed in U.S. Pat. No. 4,775,305 to Alexander and U.S. Pat. No.4,814,185 to Jones has a side tube for introduction of the resin. Theuse of vacuum to aid the resin injection is explored in U.S. Pat. No.4,820,148 to Anderson and U.S. Pat. No. 4,919,602 to Janszen. Otherrelated patents are U.S. Pat. No. 4,419,305 to Matles and U.S. Pat. No.4,385,879 to Wilkinson.

There are windshield repair apparatus of a number of different designs.In each case the objective has been to repair a stone-break by use ofvacuum and injection of resin. One type of system uses air pumps andcompressors. However, the simplest type of system is a piston andcylinder arrangement. For example in the Werner patent U.S. Pat. No.3,993,520 mentioned above, an injector is described which has an outerhousing with an interior recess in which a rubber sleeve is mounted. Therubber sleeve is taught to be used to seal against the windshield fordesired sealing by means of a protruding end portion. The injector alsohas a pressure screw which is inserted inside the housing. Inside thehousing are threads which mate with threads fin the pressure screw.Also, the pressure screw as a plunger end that fits the sleeve. Both thehousing and the pressure screw have knurled handles, the first forsetting up the apparatus, the second for injecting resin in the break.

For a normal bullseye type stone-break approximately 1 cc of resin isneeded, according to the Werner patent. This is equivalent to 3-4 dropsof resin, an amount sufficient to repair most stone breaks.

The piston-cylinder injectors of which the one shown in the Wernerpatent is typical have a number of deficiencies. Most importantly, whilethey are adequate for stone break repair; they are deficient for longcrack repair, primarily because they do not hold enough resin. Also,they are susceptible to loosing seal when the piston is backed-off toofar; and they are difficult to manipulate with the ease and precisiondesired for long crack repair.

As far as is known, the background art discussed above was designed forstone breaks rather than long cracks (over six inches). Short cracks areseen as small dots on the surface of the glass, or as a bullseye, astar-break, a combination bullseye and star break, and sometimes asvariants on these configurations. It is well known that stone breaks are"unsurfaced" that is they extend below the surface of the glass; or ifthey do extend to the surface they are so tight that they must betreated as unsurfaced when being repaired. Thus the prior repair methodsand equipment employ application of vacuum at an entry location which isthe impact spot which caused the damage, followed by injection of resinunder pressure to flow into the crack. This is called "stone damageart". In this manner the resin replaces the air in the crack. However,stone damage art cannot be used to repair cracks which are "surfaced",that is where the crack is open at the surface of the glass. Such crackshave been consistently referred to in the art as over 6 inches inlength. There has been an inability to effectively repair cracks over 6inches, and a long felt need for a method and equipment to do so. Stonedamage art employs resin viscosity normally in the range of 10-30c.p.s., but not exceeding about 50 c.p.s. In general the viscosity mustbe low enough to easily flow in the tight cracks around a stone break.Thus a thin watery viscosity has been desired.

Most such long cracks have an end which terminates at a location on theglass area which is neither the edge nor the point of impact. Thistermination location is called a "point". The point itself is very tightand locally may be unsurfaced. Further most such long cracks will extendfrom a point to the edge of the glass with an impact locationintermediate these ends. Other such long cracks will radiate from animpact location to the glass edge or to a point. Frequently the crackwill extend in two opposite directions from an impact point, ending in apoint in one direction and at an edge in the other direction. Somecracks terminate at a point at each end. Sometimes a Y formation willappear. A surfaced crack will usually be unsurfaced immediatelyproximate a point.

Various resins have been in use and introduced in the field ofwindshield repair from the early 1970's. Most of the resins, as notedabove were designed to repair stone breaks and were of low viscosity.Resins up to about 90 c.p.s. were recommended for use in hot weather,although this implies a much lower viscosity when applied to a repair asheat dramatically reduces viscosity. Over about 18 years, despite someattempts to do so the repair of cracks over 6 inches in length wasgenerally considered unsuccessful, and was disclaimed or discouraged.Therefore, crack repair was limited to 6 inches until introduction byUltra Bond, Inc. of the method disclosed in U.S. Pat. No. 5,116,441 ofwhich the present patent is a continuation-in-part (through anintermediate application).

Although in general it has been understood as explained herein that ashigh viscosity as possible should be used in the various portions of along crack, there is a disadvantage in using very high viscosities inthat the resistance to flow challenges the skills of the technicians andpresents difficulty in the presently available insertion equipment. Forexample, while one end of a crack may call for 20-60 c.p.s. resin, theother end may call for 4,000 c.p.s. An exemplary gel type resin has20,000 c.p.s. viscosity. Therefore, there is a need to determine theavailable range of viscosity, in effect while it is generally the goalto use the highESt viscosity possible, in each portion of the crack, ithas now been found that there is lower limit to the viscosity which canbe successfully used. Thus a higher viscosity should be used asspecified herein, but the lowest viscosity which will work should beselected.

DISCLOSURE OF THE INVENTION

In accordance with an embodiment of the present invention, a kit isdisclosed having bars, suction cups, pressure bolts, nuts and aninjector assembly. The injector assembly has a piston operating in acylinder. The piston has O rings that effect a seal with the cylinderwalls. The cylinder is used to hold the resin and has an O ring at itslower end which bears upon the glass. The parts of the kit may beassembled into three glass repair tools.

The first is a repair bridge tool. This tool has two suction cups forholding a frame, made of two bars, on the glass. It has an injectorassembly for injecting resin into the glass crack and it has a nylonpressure bolt which, in conjunction with the vacuum cups, holds theinjector assembly O ring firmly against the glass. The piston may berotated away from the glass to create a vacuum for removal of air from acrack or it may be rotated towards the glass to exert pressure on theresin. The pressure causes the resin to flow into the crack.

A second tool which may be assembled from the kit is the crack opener.The crack opener has a bar, two suction cups and a pressure bolt. Thesuction cups hold the crack opener on the glass. The pressure bolt maythen be rotated downward into contact with the glass. When used on theinner side of a windshield the crack opener causes the crack to open sothat resin may be injected with the repair bridge.

A third tool, that may be assembled from the glass repair kit, is therepair bar tool. This tool is similar to the repair bridge except it hasa simpler frame of a single bar. The repair bar may also be used toremove air from a crack or inject resin into a crack. It may be used inconjunction with a repair bridge tool.

In accordance with an aspect of the present invention, methods of use ofthe glass repair kit are disclosed. One method is used to fill cracks inthe outer glass layer of a windshield that extend from a point to theedge of the glass. A small bullseye is created at the point of the crackto relieve stress on the point. The bullseye is created by impacting theglass with a pointed object. A repair bridge is used to first vacuum airout of the bullseye and then to fill the bullseye with resin.

A crack opener reel is then installed on the inside of the glass to openthe crack near the bullseye. The repair bridge may then be slid alongthe crack with the crack opener to the glass edge. The pressure on theresin in the injector assembly causes the resin to flow into the crack.The resin is covered with plastic tabs to contain it and irradiated withultraviolet light to cure it, after which the plastic tabs may beremoved.

In accordance with another aspect of the current invention a secondmethod of use of the kit to fill a crack running from a point to theglass edge is disclosed. In this method of use the crack opener tool isemployed to open the crack near the point. The repair bridge is thenused to fill the crack with resin by starting at the glass edge andsliding towards the point. A bullseye is created by impact at the pointafter which the repair bridge is used to pull air from the bullseye and,finally, to fill the bullseye and the crack portion near the point withresin. The resin is retained and cured as before.

Two repair bridges are utilized in a third disclosed method of use. Abullseye is created by impacting the glass at the point of the crackwith a pointed tool. One repair bridge is mounted over the bullseye andset so as to draw a vacuum on the bullseye. A crack opener tool ismounted on the inside of the glass near the bullseye to open the crack.A second repair bridge is employed to fill the crack with resin startingat the glass edge. The second repair bridge fills the crack as it isslid along the crack to near the bullseye. Finally the first repairbridge at the bullseye is set to exert pressure and inject resin intothe bullseye and crack. The resin is retained and cured as before.

A fourth method of use of the repair kit is disclosed to fill a crack inthe outer glass layer which extends from a first point to a second pointrather than to the glass edge. Two crack opener tools are used near eachpoint to open the crack. A repair bridge is employed to fill the crackfrom near the first point to near the second point. A bullseye iscreated at each point and the repair bridge is used to remove air fromand insert resin into each bullseye in turn. The resin is retained andcured as before.

A further method has been discovered and is disclosed for selectingresins for use in different portions of long cracks. In particular therehas been defined the various portions of cracks and the failure modeswhen the wrong resin is used. Further there has been determined thelowest viscosity which will work effectively in long cracks undervarious climate conditions.

In this method the viscosity of the resin has been determined to be thecontrolling variable. The lowest effective viscosity is defined.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will be best understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Incorporated as part of the description, in order to illustrateembodiments and principles of the present invention, are theaccompanying drawings, wherein:

FIG. 1 illustrates the elements of a glass repair kit;

FIG. 1A is a plan view of a first bar;

FIG. 1B is an elevation view of the first bar of FIG. 1A;

FIG. 1C is a plan view of a second bar;

FIG. 1D is an elevation view of the second bar of FIG. 1C;

FIG. 1E is a plan view of a suction cup;

FIG. 1F is an elevation view of the suction cup of FIG. 1E;

FIG. 1G is an elevation view of a piston;

FIG. 1H is a plan view of the piston of FIG. 1G;

FIG. 1J is an elevation view of a cylinder;

FIG. 1K is a plan view of the cylinder of FIG. 1J;

FIG. 1L is a view along the line 1L--1L of FIG. 1K;

FIG. 1M is a plan view of a bolt;

FIG. 1N is an elevation view of the bolt of FIG. 1M;

FIG. 1P is a plan view of a pressure bolt;

FIG. 1Q is an elevation view of the pressure bolt of FIG. 1P;

FIG. 1R is a plan view of a nut;

FIG. 1S is an elevation view of the nut of FIG. 1R;

FIG. 2 is a plan view of a repair bridge tool;

FIG. 3 is a front elevation view of the repair bridge tool of FIG. 2;

FIG. 4 is a side elevation view of the repair bridge tool of FIG. 2;

FIG. 5 is a bottom plan view of the repair bridge tool of FIG. 2;

FIG. 6 is a plan view of a repair bar tool;

FIG. 7 is a front elevation view of the repair bar tool of FIG. 6;

FIG. 8 is a side elevation view of the repair bar tool of FIG. 6;

FIG. 9 is a bottom plan view of the repair bar tool of FIG. 6;

FIG. 10 is a plan view of a crack opener tool;

FIG. 11 is a front elevation view of the crack opener tool of FIG. 10;

FIG. 12 is a bottom plan view of the crack opener tool of FIG. 10;

FIG. 13 is a perspective view of a windshield with a crack;

FIG. 14A-D are a series of sectional views along the line 14--14 of FIG.13;

FIG. 14A illustrates a crack in the outer glass layer of a windshield;

FIG. 14B illustrates a hole drilled at the point of the crack of FIG.14A;

FIG. 14C illustrates tapping a bullseye in the hole of FIG. 14B;

FIG. 14D illustrates the bullseye created at the point of the crack inFIG. 14C;

FIG. 15 is a perspective view of a method of filling a crack in awindshield;

FIG. 16 illustrates the applying of means of lubrication to the vacuumcups of the repair bridge of FIG. 15;

FIG. 17 illustrates the filling of the cylinder bore of FIG. 15 withresin;

FIG. 18 is a perspective view of the applying of resin to a filledcrack, placement of tabs and irradiation with ultraviolet light;

FIG. 19 is a perspective view of a second method of filling a crack in awindshield;

FIG. 20 is a perspective view of a third method of filling a crack in awindshield; and

FIG. 21 is a perspective view of a fourth method of filling a crack in awindshield.

FIG. 22 is an exploded view of an injector for repairing long cracks.

FIG. 23 is a view of the injector of FIG. 22 in use.

FIG. 24 shows schematically a crack of the type under consideration.

MODES FOR CARRYING OUT THE INVENTION

In accordance with an embodiment of the present invention, a kit 150 isillustrated in FIG. 1 for the assembly of glass crack repair tools. Withthe parts shown a repairman can quickly assemble the glass crack repairtools needed for a crack repair. When the repair is concluded the partscan be disassembled and stored in a tool case or other convenientcarrier for transportation to the next job. It may be desirable for somerepair tasks to have available more than one of some of the parts of thekit 150. The exact number will depend upon the tools that one wishes toassemble. The parts of the kit 150 will be described first and then thetools that may be assembled from the parts will be shown.

FIG. 1A is a plan view of the first bar 40 and FIG. 1B is an elevationview of the first bar 40. The first bar 40 has a threaded hole 42 in oneend 44, a larger diameter threaded hole 46 in the other end 48 and athrough hole 50 in the middle 52. The middle 52 also has a recess 54 anda flat 56 on each side of the recess 54. FIG. 1C is a plan view of thesecond bar 60 and FIG. 1D is an elevation view of the second bar 60. Thesecond bar 60 has small diameter threaded holes 62 in each end 64 and alarger diameter threaded hole 66 in the middle 68. The middle 68 alsohas a recess 69.

FIG. 1E is a plan view and FIG. 1F is an elevation view of the suctioncup 70. The suction cup 70 has a cup 72 made of resilient material suchas synthetic rubber. The cup 70 has a cup side 74 and a side opposite76. A threaded bolt 78 extends from the side opposite 76.

FIG. 1G is an elevation view and FIG. 1H is a plan view of the piston80. The piston 80 has a knurled knob 82 at one end 84 and two O rings 86that fit into annular grooves 88 in the other end 90. The middle 92 ofthe piston 80 has a larger diameter with threads 94.

FIG. 1J is an elevation view and FIG. 1K is a plan view of the cylinder100 which has a knob 102 at one end 104 and threads 106 on the body.FIG. 1L is a view along the line 1L--1L in FIG. 1J showing a bore 108with internal threads 110 in a larger diameter. The end 112 has anannular groove 114 into which the O ring 116 fits.

FIG. 1M is a plan view and fixture 1N is an elevation view of the bolt120. The bolt 120 has a knob 122 and threads 124 on the end 126. FIG. 1Pis a plan view and FIG. 1Q is an elevation view of the pressure bolt130. The pressure bolt 130 has a knob 132 and threads 134 on the end136. FIG. 1R is a plan view and FIG. 1S is an elevation view of the nut140. The nut 140 has a knob 142 and internal threads 144 on the end 146.

Thus the kit 150 has the first bar 40, the second bar 60, the suctioncup 70, the piston 80, the cylinder 100, the bolt 120, the pressure bolt130, and the nut 140. The bolt 120, the pressure bolt 130 and the nut140 may be made of a material such as nylon that will not scratch glass.The first bar 40, the second bar 60, the piston 80 and the cylinder 100may be made of a light material such as aluminum or plastic. The bolt 78may be made of a suitable material such as steel or aluminum.

The kit 150 may be assembled into several glass crack repair tools. Oneis the repair bridge 160 illustrated in the plan view of FIG. 2, thefront elevation view of FIG. 3, the side elevation view of FIG. 4 andthe bottom plan view of FIG. 5. The repair bridge 160 is constructedwith the first bar 40 placed over the second bar 60 with the recess 54of the first bar 40 placed against the recess 69 of the second bar 60and secured with the bolt 120 which passes through the hole 50 in thefirst bar 40 and threads into the threaded hole 66 in the second bar 60.The first bar 40 is held substantially orthogonal to the second bar 60by the flats 56 of the first bar 40 bearing against the sides of therecess 69 of the second bar 60.

The bolts 78 of two suction cups 70 are screwed into the threaded holes62 of the second bar 60. The pressure bolt 130 is threaded into thethreaded hole 42 of the first bar 40.

An injector assembly 152 is constructed by threading the piston 80 intothe cylinder 100 so that the O rings 86 of the piston 80 are adjacentthe O ring 116 of the cylinder 100 when the piston 80 is threaded allthe way in. The injector assembly 152 is threaded into the largerdiameter hole 46 of the first bar 40. The cup 72, the threaded end 136of the pressure bolt 130, and the end 110 of the cylinder 100 all facethe same direction relative to the first bar 40.

The repair bridge 160 may be held on a glass surface by the suction cups70. If the cups 72 are coated with a means for lubrication such aspetroleum jelly, the repair bridge may be slid along the glass surface.By rotating the pressure bolt 130 and the cylinder 100 towards the glasssurface the O ring 116 of the cylinder 100 may be compressed against theglass surface. It may be appreciated that the piston may then be rotatedtowards the glass to create pressure in the bore 108 (FIG. 1L) of thecylinder 100 or may be rotated away from the glass to create a vacuum inthe bore 108. When a vacuum is created in the bore 108, air will bepulled from a glass crack that is surrounded by the O ring 116. When apressure is created in the bore 108, resin placed in the bore 108 willbe forced into a glass crack that is surrounded by the O ring 116.

A second glass repair tool that may be assembled from the kit 150 is therepair bar 180 illustrated in the plan view of FIG. 6, the frontelevation view of FIG. 7, the side elevation view of FIG. 8 and thebottom plan view of FIG. 9. The repair bar 180 construction begins witha suction cup 70 placed in the hole 50 and against the recess 54 of thefirst bar 40 and secured by threading the nut 140 over the bolt 78 (FIG.1F) of the suction cup 70. The pressure bolt 130 is threaded into thethreaded hole 42 of the first bar 40.

An injector assembly 152, assembled as described above for the assemblyof the repair bridge 160, is integrated in the repair bar 180 bythreading it into the larger diameter hole 46 of the first bar 40. Thecup 72 of the suction cup 70, the threaded end 136 of the pressure bolt130, and the end 110 of the cylinder 100 all face the same directionrelative to the first bar 40. As described above for the repair bridge160, the injector assembly 152 may be used to draw air from a cracksurrounded by the O ring 116 or to insert resin, placed in the bore 108(FIG. 1L), into the crack.

A third glass repair tool which may be assembled from the kit 150 is thecrack spreader 170 as illustrated in the plan view of FIG. 10, theelevation view of FIG. 11 and the bottom plan view of FIG. 12. The bolt78 (FIG. 1F) of a suction cup 70 is threaded into each of the threadedholes 62 of a second bar 60. A pressure bolt 130 is threaded into thethreaded hole 66 of the second bar 70. The cups 72 of the suction cups70 and the end 136 of the pressure bolt 130 face the same directionrelative to the second bar 60. The recess 69 of the second bar 60 isshown in FIG. 11 to also face the same direction although this isoptional.

The crack spreader 170 may be placed on the inside of a windshield withthe suction cups 70 straddling the crack in the outer glass layer of thewindshield. When the pressure bolt 130 is rotated so as to contact theglass surface with its end 136, the suction cups 70 resist by pulling onthe inner glass layer and the crack in the outer layer is caused tospread apart. This allows easier flow of resin into the crack. The crackspreader 170 can be slid along the crack just in front of the injector.

Methods of use of the embodiment of the present invention areillustrated in FIGS. 13-21. Many of the methods of use concern therepair of a crack that starts at a point and runs either to the glassedge or to another point. If the crack does run to a point rather thanto a bullseye it is advantageous to create a small bullseye at thepoint. This relieves strain on the point preventing further spreading ofthe crack and also provides an injection point for resin.

FIG. 13 and FIGS. 14A-D show the creation of a bullseye at a point. Inthe methods of use that follow, the words "tap a bullseye" or the like,will be understood to refer to this process. FIG. 13 illustrates a frontview of a windshield 200 that has a crack 202 originating at a point 204and running to the glass edge 222. To create a small bullseye at thepoint 204 the steps of FIG. 14A-D, which are a series of sectional viewsalong the line 14--14 of FIG. 13, should be followed.

In FIG. 14A the crack 202 is seen in the outer glass layer 208. Theinner glass layer 212 and the polybutyral layer 210 complete the sectionof the windshield. The first step to tap a bullseye is to drill a smallhole 218 of diameter between one sixty fourth and one fourth of an inchin diameter approximately one half to three fourths of the way throughthe outer glass layer 208 as shown in FIG. 14B. Then a means forstriking such as a small mallet 214 is used with a means fortransferring force to a point such as a sewing machine needle 216. Theneedle 216 is placed in the hole 218 and tapped by swinging the mallet214 in the direction 228 as shown in FIG. 14C. A razor blade holder mayalso be used for the means for striking. The result is shown in FIG. 1Dwhere a small cone 220 of glass has been broken loose from the outerglass layer. Consequently a passageway in ensured through the outerglass layer 208 to enable the flow of resin into the crack.

FIG. 15 is a perspective view of the windshield 200 with the crack 202running from a point (FIG. 13) to the glass edge 222. The first step inthis method of crack repair is to tap a bullseye (as described above andshown in FIG. 14) at the point of the crack 202. The piston 80 isassembled with the cylinder 100 and resin 230 is then placed through theend 112 into the bore 108 of the cylinder 100 as shown in FIG. 16. Thenumber of drops of resin 230 to use should be approximately the cracklength in inches minus two. Means for lubrication such as petroleumjelly 226 is placed on the cup 72 of the suction cups 70 as illustratedin FIG. 17. The repair bridge 160 is then placed on the glass in FIG. 15with the suction cups 70 compressed so as to hold the repair bridge 160in place. The cylinder 100 and the pressure bolt 130 are both rotateddownwards towards the glass until the O ring 116 (FIG. 1L) in the end ofthe cylinder 100 is compressed against the glass with the O ring 116centered over the bullseye.

The piston 80 is then rotated away from the glass to create a vacuum inthe bore 108 (FIG. 1L) which pulls the air out of the bullseye. Thepiston 80 is then rotated towards the glass and the pressure on theresin in the bore 108 causes the resin to flow into the bullseye andpart way down the crack 202. Means for applying pressure such as thecrack opener 170 is placed on the inside of the windshield 200. Thepressure bolt 130 of the crack opener 170 is rotated towards the glassuntil it and the suction cups 70 of the crack opener 170 have appliedenough force to open the crack slightly.

The repair bridge 160 and crack opener 170 may then be slid along thecrack 202 in the direction 224 to the edge 222 keeping the O ring 116centered over the crack 202. The crack 222 will fill with resin forcedout of the bore 108 by the pressure exerted by the piston 80. The repairbridge 160 and the crack opener 130 are then removed from the glass.

Resin 230 is then spread over the bullseye and the crack 202 as shown inFIG. 18, which is a perspective view of the windshield 200, and meansfor retaining the resin such as plastic tabs 232 are placed on the resin230. The plastic tabs serve to keep air out of the crack and help itcure faster. Finally, the resin 230 is irradiated with ultraviolet lightfrom an ultraviolet source 234 to cure it. The tabs 232 may then beremoved and excess resin removed with a blade. Finally the glass may becleaned with a glass cleaner being careful to not get cleaner on thefresh resin.

In FIG. 19 a second method of filling a crack 202 in a windshield 200 isillustrated. A crack opener 170 is placed on the inside of thewindshield 200 one to four inches from the point 204. The pressure bolt130 is rotated towards the glass until the crack is opened slightly. Thesuction cups 70 of a repair bridge 160 are coated with petroleum jellyas shown in FIG. 17. The piston 80 and cylinder 100 are assembled andresin 230 is placed in the end 112 of the bore 108 as shown in FIG. 16.The length of the crack in inches less two is the number of drops ofresin 230 to use.

The repair bridge 160 is placed at the edge 222 of the crack 202 and thecylinder 100 and pressure bolt 130 turned towards the glass until the Oring 116 (FIG. 1L) is compressed against the glass and centered over thecrack 202 at the edge 222. The piston 80 is turned towards the glass tocreate pressure on the resin in the bore 108. The repair bridge 160 isthen slid along the crack 202 in the direction 240 keeping the O ring116 centered over the crack 202 so as to fill the crack 202 with resin.Stop the repair bridge with the O ring 116 one to three inches from thepoint. The last part of the crack is the tightest and thus hardest tofill.

The repair bridge 160 and crack opener 170 are then removed from theglass. Resin 230 is then spread over the filled portion of the crack 202as shown in FIG. 18 and plastic tabs 232 are placed on the resin 230.Finally, the resin 230 is irradiated with ultraviolet light from anultraviolet source 234 to cure it.

A bullseye is tapped at the point 204 as described above and shown inFIGS. 14A-D. The repair bridge 160 is then placed on the glass as beforebut with the O ring 116 centered over the bullseye. The piston 80 isthen rotated away from the glass to create a vacuum in the bore 108(FIG. 1L) which pulls the air out of the bullseye. The piston 80 is thenrotated towards the glass and the pressure on the resin in the bore 108will cause the resin to flow into the bullseye and part way down theremaining portion of the crack 202.

The repair bridge 160 is then removed from the glass. Resin 230 is thenspread over the bullseye and the remaining portion of the crack 202 andplastic tabs 232 are placed on the resin 230 as shown in FIG. 18. Theresin 230 is irradiated with ultraviolet light from an ultravioletsource 234 to cure it. The tabs 232 may then be removed and excess resinremoved with a blade. Finally the glass may be cleaned with a glasscleaner being careful to not get cleaner on the resin.

A third method of repairing glass cracks is illustrated in FIG. 20. Itdiffers from the second method just described in that a bullseye isinitially tapped at the point 204 of the crack 202 (FIG. 19). Then asecond repair bridge 160' with resin 230 in the cylinder 100' (as inFIG. 16) is placed over the bullseye and the piston 80' is turned awayfrom the glass to create a vacuum over the bullseye. The second repairbridge is left at the bullseye and the remainder of the repair proceedsas described above in the second method and as shown in FIG. 19. Afterthe first repair bridge has been slid in the direction 242 to fill thecrack 202 to within one to three inches of the bullseye, it is removedfrom the glass. The piston 80' of the second repair bridge 160' isturned towards the glass to create pressure on the resin 230 in thecylinder 100' which will cause the bullseye and the remaining portion ofthe crack 202 to fill with resin 230. The spreading of resin 230 overthe filled crack and bullseye, placement of tabs 232, irradiation withan ultraviolet light source 234 and cleanup with a blade and windowcleaner is as described for the second method and illustrated in FIG.18.

A fourth method of repairing a glass crack 202 in a windshield 200 isillustrated in FIG. 21. In this case the crack 202 runs from a point 204to a second point 204'. Two crack openers 130 and 130' are placed on theinside of the glass one to four inches from each point to open the crack202 in a method previously described. A repair bridge 160 is used alongthe direction 244 as previously described in the other methods to fillthe crack to within one to three inches of each point 204, 204'. Abullseye is tapped at each point 204, 204'. The repair bridge 160 isthen used to remove air from one bullseye and fill it with resin. Thisis repeated at the other bullseye. Covering with resin, placement ofplastic tabs, radiation with ultraviolet light, and cleanup is aspreviously described for other methods and as shown in FIG. 18.

In the methods for filling glass cracks described above, means forapplying pressure were used to spread the glass crack near the point ofthe crack to make it easier to inject resin into the crack. It wasdisclosed that a crack opener 170 as shown in FIG. 10 may be used. Arepair bridge 160 (FIG. 2) may also be used as may the hands, thumb orfingers of the repair man. It helps, if using the hand or thumb to coatwith means for lubrication, such as petroleum jelly so the pressure canbe moved smoothly along the glass.

In the methods for filling glass cracks described above and, it shouldalso be appreciated by those skilled in the art that the repair bar tool180 (FIGS. 6, 7, 8 and 9) may be substituted for the repair bridge tool160 (FIGS. 2, 3, 4 and 5) where desired. The repair bar tool 180 mayalso be substituted for one or both repair bridge tools 160 where tworepair bridge tools 160, 160' were used, as in the third method shown inFIG. 20.

Resin 230 (FIG. 16) is available in a range of viscosities. In generalas high a viscosity as possible should be used because the completedrepair will be more likely to remain clear of spots and lines ofrefraction. High viscosity also keeps the repair from splitting apartdue to temperature changes and stress. However, because it is hardest toget the resin to flow near the point of a crack, lower viscosity resinmay be used there. The colder the climate, the higher the viscosityshould be. When performing crack repairs in cold weather the glass mustbe warmed gradually before starting.

The cure time, which is the time during which the resin is irradiatedwith ultraviolet light, is five to seven minutes. If, after curing, athin line of refraction appears, this can be resolved by drilling intothe crack in the middle of this line and using the repair bridge 160 inboth the vacuum and pressure mode to inject resin.

Sometimes the crack does not come to the surface of the glass. In thosecases a hole should be drilled into the crack and a bullseye tapped.Then a repair bridge 160 may be placed over the bullseye in the pressuremode. Another hole is drilled three to four inches further down thecrack and another bullseye tapped. Another repair bridge 160 or a repairbar 180 is placed over this bullseye in the vacuum mode. This will causeresin to flow from the first bullseye to the second. This process may berepeated down the crack to fill all of it.

FIG. 22 shows in an exploded view another embodiment of a pistoncylinder injector; and FIG. 23 shows this embodiment installed for usein the second glass repair tool previously shown in FIGS. 6, 7, 8 and 9.

Referring to FIGS. 22 and 23 the injector 300 has three main parts, apiston 302, a piston cap 304 and a cylinder 306. When assembled for use,the piston 302 and the piston cap 304 become a single piston assembly308 for use with the cylinder 306.

The piston 302 has an exterior threaded screw end 310, an upper shaft312, a lower shaft 314, a first shouldered neck-down portion 316 and asecond shouldered neck-down portion 318. Each neck-down portion 316 and318 are adapted to receive O-ring seals 320 and 322 (FIG. 23)respectively as shown in FIG. 23.

The piston cap 304 is a cylinder having a knurled exterior 324 and aaxial through-hole 326. At the upper end of the through-hole 326 arethreads 328 which extend a relatively short length and are mateable withthe threads 329 on the piston 302 so that together they become thepiston assembly 308. The rest of the through-hole 326 has threads 330,of smaller diameter than threads 328.

The cylinder 306 has a through-hole 332 which may be a single bore size;but in this case has an upper bore 334 of larger diameter than the lowerbore 336. The size of the lower bore 336 is set to provide good sealwith the O-ring seals 320 and 322. The lower bore 334 defines acontainment volume for resin as will be explained below. At the bottomopening of the lower bore 336 is a seal seat 338 in which is fitted anO-ring seal 340 as shown in FIG. 23. The exterior of the cylinder 306has an upper threaded portion 342 which threadably mates with threads330 in the piston cap 304; lower threads 344, and a knurled knob 346which is about midway of the cylinder 306.

FIG. 23 shows the injector 300 mounted onto the tool 348 by threadingthe lower threads 344 into mating threads 358 in the tool 348. The tool348 is the same as described above, but substituting the injector 300,for the injector previously described.

The injector 300 is generally used as described for the injectorassembly 152 but with particular advantages for use in repairing longcracks. Prior injectors can hold about 1 cc of resin which is about 3 to4 drops. However, the injector 300 has a capacity to hold in thecontainment volume of the lower bore 336 about 22 to 24 drops which isenough for a 24 inch crack. FIG. 23 shows the piston withdrawn to itsuppermost position, providing the maximum containment volume 352 forresin 353. Also, in this position the upper thread 340 is just showingoutside the bottom end 354 of the piston cap 302. This gives a visualsignal to the user, of the uppermost position for withdrawal of thepiston assembly 308 in the cylinder 306. Also, a series of marks asshown at 356 could be put in place on the outside surface of thecylinder 306 to visually indicate a withdrawal position sufficient togive a containment volume for selected amounts of resin consistent withrepair of specified crack lengths such as 10 inches, 15 inches, 20inches etc. Of course the skilled technician can use these marks asguidance for any length of crack within the capacity of the injector.

The knurled knob 346 is used to adjust placement of the O-ring seal 340on the glass 358 for flatness and tight seal. After that adjustment, forrepairing long cracks, the entire tool will be slid along the crack(being careful to avoid touching the crack with the suction cup) and thepiston assembly 308 will be turned to inject resin to fill the crack asthe sliding progresses. As the piston cap 304 exterior diameter can bequite large, very precise feel and control of the resin injection rateis possible.

In this construction the end of the lower portion of 314 of the piston,that is where the O-rings 320 and 322 are situated is a long distancefrom the area of the threaded mating of the threads 330 and 342.Therefore, with the tolerances allowed in the thread mating, the end ofthe piston has sufficient play or allowable movement that, when ridingin the lower bore 336, the O-ring 320 and 322 can self-center. There areno forces tending to force the O-rings unsymmetrically against the wallof the lower bore 336. This will ensure the best seal and long life forthe O-rings 320 and 322. In this case the threads 342 and 330 are 1/2-13threads. This gives the desired play at the end of the piston 314. Italso allows a convenient rate of injection of fluid as the pistonassembly 308 is turned. Also, the engagement of threads 342 and 330 isfixed in length because the threads 342 has only a limited length. Inthis case threads 342 are 5-6 turns or rotations and threads 330 hasabout 17 turns or rotations. Thus the extent of engagement is fixed tothe 5-6 thread turns of threads 342 and the force needed to turn thepiston in or out is constant. Also, since threads 342 are on the outsideof the piston 306, they are of relatively large diameter (1/2 inch)which allows a loose tolerance. There, the major resistance to turningis presented only by the fit of the O-rings 320 and 222 on the lowerbore 336.

The threads 344 are finer, in this case 1/2-20. These threads need tohold tightly once set to the proper position so a thread of tighterengagement is needed. Also, a finer movement is needed to be able to setthe injector tightly and flat against an item of glass to be repaired asshown in FIG. 23.

Therefore, the injector 300 can be used for both stone damage and longcracks. It will hold a large amount of resin when the piston assembly isbacked full out as shown in FIG. 23. The tip of the lower piston shaft314 is self centered due to the distance away of the threads 342 fromthe piston tip where the O-rings 320 and 322 are located and alsobecause threads 342 are substantially larger in diameter than thediameter of the tip of the lower piston shaft 314 and are of relativelycoarse, low tolerance threads. Therefore very little resistance toturning the piston assembly 308 is contributed by the thread engagementof threads 342 and 330, which in any case is constant. A greater butstill constant resistance to turning is consistently contributed byengagement of the O-rings 320 and 322 on the lower bore 336.

The construction allows the outside surface 324 of the cap 304 to be aslarge diameter as desired, allowing precise control of the turningmovement for resin injection. Therefore, with a minimum amount oftraining and experience an operator can inject resin uniformly into acrack while moving the tool along the crack, and at the same timeprecisely turning the piston assembly, to inject resin.

The knob 346 is also of relatively large diameter in order to allowprecise turning of cylinder 306. However the knob 346 should be largerin diameter than the cap 340, for the reasons given below.

To use the injector 300, the piston assembly 308 is backed off toprovide a resin containment volume of the desired volume. Holding theopening (where the seal seat 340 is) up, resin is inserted into thecontainment volume. Then the O-ring 340 is put in place and the pistonassembly 308 rotated, if necessary, until the resin is at the O-ring340. At this point there should be no air in the containment volume,only resin.

The tool 348 is already generally in place near the crack, and if used,a crack opener is in place. The injector 300 is threaded into thethreads 358, the tool having been placed previously over the crack. Theinjector is rotated by knob 346 to be well scaled and flat on the glass.The larger diameter of knob 346, that is, larger than the diameter ofthe cap 304 enables easy adjustment without interference from the cap304 and without disturbing the position of the cap 304.

When resin is being injected the cap 304 is turned the bottom 354 of thecap 304 will hit the knob 346, to prevent further travel of the lowerpiston shaft 314 when it is just short of projecting beyond the end ofthe through hole 332, that is, just at or short of the seal seat 338.

In use for long cracks, it is preferred to use only the bar shapedsingle suction cup supporting tool of FIGS. 6, 7, 8 and 9, rather thanthe double suction cup tool of FIGS. 2, 3, 4 and 5. This gives bettercontrol for smooth even sliding along the crack, with one hand, whileturning the cap 304 with the other hand; thereby resulting in a wellcontrolled volume of resin injection to just, but fully, fill a crack.The crack may vary in width, thus requiring variable rate of injection,but preferably with constant rate of sliding over the crack. Therefore,the present tool and injector combination allow the precise smoothaction both in sliding and rate of injection. Also, the single suctioncup will have less pull on the glass; too much pull can move the glass,which is detrimental to a good result.

If more pressure is needed the knob 346 can be turned easily to provideit.

Also, this injector 300 can be operated alone, without a supporting toolby holding it firmly in place and sliding, with one hand, and turningthe cap 304 with the other hand.

As stated above, for best repair of long cracks, that is surfacedcracks, it is best to use the thickest, that is the highest viscosityresin which can be employed. Also, in a colder climate viscosity shouldbe higher than would be used in a warmer climate.

Therefore in a moderate climate for cracks of increasing openness, theresin viscosity may extend in a range from about 60 c.p.s. to about1,500 c.p.s. In a cold climate for cracks of increasing openness, theresin viscosity may extend in a range from about 60 c.p.s. to 4,000c.p.s. The reason for this is that the higher the viscosity in mostresins (e.g. aerobic, two-part and U.V.) the greater will be the holdingpower. This holding power is needed with windshields during thermalexpansion and contraction cycles. Warming of the resin for the injectionprocedure will make injection easier.

Holding power refers to adhesion of the resin to the glass as well as tothe internal strength and elasticity of the resin. After curing athicker (higher viscosity) resin gives a more clear even appearance withless possibility for air spots being formed during injection.

The choice of viscosity varies with climate, length of crack andlocation of crack on a windshield. Following are some examples:

EXAMPLE #1

Climate: Southern California

Length: About 12 inches or less

Location: Side of windshield

Resin: At the point, as low as about 40 c.p.s. Remainder about 60 c.p.s.

EXAMPLE #2

Climate: Southern California

Length: About 18 inches

Location: Side of windshield

Resin: At the point, about 60 c.p.s. Remainder about 90 c.p.s.

EXAMPLE #3

Climate: Southern California

Length: About 18 inches

Location: Bottom of windshield

Resin: At the point, about 60 c.p.s. Near the edge, about 1,500 c.p.s.Intermediate area about 500 c.p.s.

EXAMPLE #4

Climate: Chicago (i.e. cold winter)

Length: About 12 inches

Location: Side of windshield

Resin: At the point, about 60 c.p.s. Remainder about at least 150 c.p.s.

EXAMPLE #5

Climate: Chicago (i.e. cold winter)

Length: About 18 inches

Location: Side of windshield

Resin: At the point, about 60 c.p.s. Remainder about at least 1,200c.p.s.

EXAMPLE #6

Climate: Chicago (i.e. cold winter)

Length: About 18 inches

Location: Bottom of windshield

Resin: Near the edge, about 3,000 c.p.s. Intermediate, about 1,200c.p.s. At the point about 60 c.p.s.

Further investigation has resulted in additional discoveries respectingthe use and choice of resins in various conditions and methods ofrepairing cracks using various resins.

In part the additional invention resides in discovering and defining thevarious modes and types of failure, in considering the needs andcapabilities of workers in the field to be able to effectively madegood, lasting repairs and in determining the controlling resin variableor variables in making effective repairs in long cracks.

In particular, although it has been determined that use of the highestpossible viscosity of resin is desirable in each portion of the repairin order to ensure the greatest integrity of the repair, there aredisadvantages to this procedure. In particular, high viscosity resinsare more difficult to use. Also, it should be appreciated that the wallsof the glass in a crack have small crevices, pits and similardiscontinuities. Ultimately at very high viscosity, the flow resistancecauses the resin to fail to fill all these crevices and pits andtherefore establish an incomplete adhesion in which integrity of thebond is compromised between the resin and the crack wall is compromised.Therefore, within the notion that higher viscosity resin should be usedin the open part of the crack it is desirable to find the lowestviscosity which will be effective. In the investigation necessary forthe present invention, it was necessary to define the various types andportions of cracks, and to define the difference between success andfailure in a repaired crack.

As noted above, long cracks (over 6 inches in length) have a surfacedportion which is repaired by progressive insertion of resin from thesurface, also referred to as sliding surface injection of resin. Mostsuch long cracks extend to the edge of the windshield. The crack iswidest nearer to the edge of the windshield and is narrower as itprogresses to a point in the glass area. Also, a crack that proceeds tothe edge will be substantially wider than an equivalent length crackwhich does not. Also, the longer the crack, the wider it is at theextreme open end.

Cracks appear in different parts of the windshield, and the position ofthe crack will effect the repair requirements. In particular a crackthat ends at the bottom of the windshield is more problematic because itis subject to greater vibration and change in gap due to temperaturecycling such as when the defroster is in use. Cracks at the side and topare less problematic.

The elements of a crack are defined as a point portion and a remainderportion and within the reminder portion an edge portion and anintermediate portion. FIG. 24 shows schematically a crack of the typeunder consideration. This shows the point portion, the remainderportion, the edge portion, and the intermediate portion. Because of theway windshields are curved and stressed especially in the curved portionof the glass, the crack is much wider at the edge and 95% (a roughestimate) of all cracks over 6" in length will run to the edge. In factwhen observed, a crack which proceeds to the edge will make a cracklingor clicking sound and can be seen when magnified to open substantiallywhen the crack reaches the edge.

The point portion terminates in the glass area and is either unsurfacedor very tight. The point portion is, in general, that portion whichstanding alone would fall within the scope of "stone damage" and wouldbe repairable with stone damage art as described previously.

Most of the time in a long crack the impact point will appear in theremainder portion. If the impact point is a bullseye, star orcombination, that portion will be repaired by stone damage pressuretechniques, such as point pressure injection. Often the impact pointwill be very small, such as the size of a pin head, and can be ignored.

While the flow of resin into the point portion will normally beaccomplished by point pressure injection into a passageway and thencealong the crack interior, in some cases the point portion can be filledby sliding surface injection. For example, if the viscosity of theselected resin is very thin such as 10-20 c.p.s. it may flow into even atight surfaced crack. Or, if the crack is flexed from inside thewindshield an unsurfaced crack may surface and open and a tight surfacedcrack may open enough for sliding surface injection of a thin resin.Sliding surface injection is easier than point pressure injection if theright tools are used.

The remainder portion of the crack is surfaced, and is relatively widerthan the point portion presenting sufficient gap that it is repairableby sliding surface injection. The remainder portion is typically in thatpart of the crack which extends from the point portion to the edge ofthe glass. These typical forms are described but cracks can take manydifferent forms. However, it is normally expected to see a point portionand a remainder portion in a crack over 6 inches in length. When a crackgoes to the windshield edge it opens much more than when it does not,and therefore it is useful to define the intermediate portion and theedge portion of the remainder portion. The intermediate portion extendsbetween the point portion and the edge portion. The edge portion extendsto the edge of the windshield. The edge portion will be substantiallywider than the intermediate portion. In a 12 to 18 inch crack it wouldbe expected that the edge portion would extend 1 to 6 inches in lengthdepending on the crack location and configuration. Although thesedefinitions are imprecise, in application to a particular crack, thereare consistent features to be seen. The point portion is defined above.The intermediate portion has a gap of not unusual width. The edgeportion is noticeably wider. In some cases there will be little or nointermediate portion; in other cases the edge portion may be of notunusual width. Defining these portions is important to aid thetechnician in recognizing them so as to analyze the crack and determinethe optimal repair procedure. The definitions are also important inorder to specify the process.

It has been found that faults in a long crack repair can becharacterized as follows:

Separation. This is separation of the resin from the plastic layer atthe bottom of the crack. Separation will appear as refraction in theform of short spots or longer lengths (sometimes called a "runner").Separation can occur immediately such as during curing of the resin, orit may occur within a few days. In the latter case it is considered aform of deterioration as noted below. Immediate separation is normallyrepaired immediately as part of the initial repair.

Deterioration. In this form the fault appears either in the body of theresin or by detachment of the resin from the crack either at the sideswhere it adheres to the glass or the bottom where it adheres to theplastic laminate. The resin will pull apart or will be pulled away fromits adhesion to the glass in the crack or pieces of resin may come offthe exterior surface of the resin may be damaged. Also later separationis a form of deterioration. Deterioration is a later effect which occursafter the repair is completed, usually due to physical disturbance ofthe resin. It may occur gradually. The most common cause ofdeterioration is thermal expansion and contraction of the windshield.Physical affects such as windshield wiper, dirt accumulation, ice orfrost or ice scraping or vibration or flexing of the windshield are alsocauses of deterioration. Two types of deterioration were observed. Edgedeterioration appears commencing at the edge of the glass inward and ischaracterized by resin pulled out of adhesion to the glass, splittingapart of the resin body. Top surface deterioration is where the surfaceof the resin is jagged or galled, possibly small pieces missing, andspots of refraction appear.

It should be noted that if there is dirt in a crack, edge deteriorationis more likely, therefore mixed results in a plurality of tests could beassociated with occasional dirty cracks.

Failure. In this fault, after the repair, the crack itself extendsfurther than originally, past the terminal end of the point portion intonew glass area. This is a later effect. A crack which "holds" is onewhich did not fail.

As for the length of the crack, in theory any length crack can berepaired. The bonding strength of the resin will be sufficient torestore the windshield. But, it has been found that when a crack exceeds18 inches, a different set of problems often appear. Such long cracksare often the result of extension of an older shorter crack.Consequently, such a crack will be dirty, due to its age, and repair isnot recommended unless sufficient cleaning of the crack can be ensured,or if it is relatively new and clean. Cleaning can be done by injectinga cleaning solvent into the crack and blowing it out with compressedair.

In general the primary factors to be considered in choosing the resinsto be used in a crack repair are the immediate and the lasting qualityof the repair. The immediate quality concern is basically how the repairlooks after it is finished, that is that the crack be completely filledwith resin leaving no air gaps or bubbles. The resin must be in completecontact with the sides and bottom of the crack. There must be no bubblesin the resin itself. Overall the goal is to eliminate any refractionsurfaces to minimize or eliminate light refraction. As noted aboveseparation can be an immediate quality factor because it can occur asearly as during curing or shortly thereafter. This concern is effectedby the flow quality of the resin, that is its viscosity, the tools used,and the operator's skill.

The lasting quality concern is that a well executed repair remain so. Ithas been found that the mechanisms for poor lasting quality can becharacterized as separation, deterioration and failure as defined above.

The characteristics of resins which are known to purchase are: adhesionstrength, tensile strength, and viscosity. Resins are also characterizedby a manufacturer as being adhesive type or structural adhesive type. Ithas been determined by the test and examples herein that viscosity cansufficiently define the desired quality of the resin to accomplisheffective repairs.

The appropriate viscosity in terms of immediate quality of repair isrelatively easy to ascertain, it is a viscosity that can be easilyinserted, will flow smoothly and readily, will enter the crack readilyand will fully fill the crack including the pits and its crevices.

But, the lasting quality concerns are less easily apparent. Although itis appreciated as noted above that the highest viscosity possible shouldbe used in various portions of a crack, in order to ensure an effectiverepair, there is a disadvantage in this applying this conclusion. Quitehigh viscosities are available. But the severe resistance to flow andconsequent unpredictability of flow confronts the varying skills of theoperating technicians and the capabilities of the equipment used toinject the resin. Thus it is desirable to use not the highest viscosityresin available or even which is flowable into the crack, but rather thelowest viscosity which will still provide an effective repair.

The point portion will still employ the stone damage techniques of thepast, using very thin resins to enable flow into an access passagewaysuch as an impact point or drilled access passageway, or to flow into atight but surfaced portion. The highest viscosity which can be used inthe point at room temperature is usually about 80 c.p.s. with somedifficulty. 40-60 c.p.s. works best for ease of use and 90-100 c.p.s.can usually only be used in temperatures exceeding 85° F. 40-60 c.p.s.will hold and will not deteriorate in the point section. Under 40 c.p.s.will have separation from the lamination too often. 40-80 c.p.s. isrecommended with 40-60 c.p.s. being the easiest. A series of tests wereconducted. The test data and results are shown in Table I, and aredescribed below.

                                      TABLE I                                     __________________________________________________________________________    VISCOSITY                                                                            ADHESIVE                                                                             TENSILE       DETERIORATION                                                                            FAILURE IN                                                                            FAILURE IN FOUR                C.P.S. P.S.I. P.S.I.                                                                              SEPARATION                                                                            EDGE/TOP** SO. CALIF.                                                                            SEASON CLIMATE                 __________________________________________________________________________     10    1500   7000  YES     YES/YES    YES     PRESUMED                       10-15  1850   2100  YES     YES/YES    YES     PRESUMED                       15-20  1800   2000  YES     YES/YES    YES     PRESUMED                        20    1500   10000 YES     YES/YES    YES     YES                             40    1500   10000 YES     YES/YES    YES     YES                             40    1800   2800  YES     YES/YES    YES/NO* YES                             60    1500   10000 YES     YES/YES    YES/NO* YES                             80    1500   6600  YES     YES/YES    YES/NO* YES                            100    1800   2800  YES     YES/YES    NO      NO                             120    1500   2700  YES     YES/YES    YES     YES                            150    1500   10000 NO      SLIGHT/SLIGHT                                                                            NO      NO                             200    l500   4000  NO      NO/VERY SLIGHT                                                                           NO      NO                             300    1500   4000  NO      NO/NO      NO      NO                             400    1500   4000  NO      NO/NO      NO      NO                             500    1500   4000  NO      NO/NO      NO      NO                             600    1500   4000  NO      NO/NO      NO      NO                             800    1500   4000  NO      NO/NO      NO      NO                             1000   1500   10000 NO      NO/NO      NO      NO                             1200   1500   10000 NO      NO/NO      NO      NO                             1500   1500   12000 NO      NO/NO      NO      NO                             1800   3000   4000  NO      NO/NO      NO      NO                             3600   2500   5200  NO      NO/NO      NO      NO                             4000   4000   6000  NO      NO         NO      NO                             __________________________________________________________________________     ** EDGE means at the edge of the glass TOP means at the top surface of        resin                                                                         *YES/NO -- HELD CRACKS FROM THE TOP AND SIDES BUT NOT OFF THE BOTTOM OR       FAILED WHEN THERE WAS A FROST OR DEFROSTER USE.                          

The table records viscosity of resin as specified by manufacturers whichis understood to be specified at room temperature. Some of the resinswere prepared by mixing other compatible resins to arrive at a desiredviscosity. The table also records adhesive strength and tensile strengthof resins. Repaired windshields were examined at least three monthsafter repair. The table records the presence or absence of variousfaults:

Separation.

Deterioration of the resin at the edge portion of the crack and at thetop surface of the resin.

Failure in Southern California--repairs were done at room temperature orabove and vehicles operated in Southern California.

Failure in Four Season--repairs were done at below room temperature andvehicles were operated in cold climate.

It is generally considered that higher viscosity resins will have ahigher tensile strength, but this is not the case as can be seen in theTable I in which for example 20 c.p.s. and 40 c.p.s. samples had a10,000 p.s.i. tensile. In any case the test data shows that tensilestrength is not consistently variable in deterioration of repairsalthough it appears to have some effect and may be relevant. But, forpurposes of determining the choice of resin, the tests confirm thatviscosity is consistently the controlling specification. The 20 c.p.s.viscosity resin with a tensile strength of 10,000 p.s.i. and 1,500p.s.i. adhesion strength would not hold while a resin of 800 c.p.s.viscosity 4,000 p.s.i. tensile strength and 1,500 p.s.i. adhesivestrength did hold and also did not deteriorate. Also, the 100 c.p.s.resin having 2,800 p.s.i. tensile deteriorated. The 150 c.p.s. resinwith 10,000 p.s.i. deteriorated slightly; at 200 c.p.s. the resultimproved to an acceptable level and at 300 c.p.s. there was nodeterioration. The tests demonstrate that viscosity is the primarycontrolling quality to be considered in choosing resins for use in theremainder portion of a long crack. However, when the viscosity is raisedthe repair is better regardless of the slight adhesion strengthvariation. This interpretation relies on the 100 c.p.s., 120 c.p.s. and150 c.p.s. samples. Long term observation has lead to the conclusionthat the 120 c.p.s. samples were possibly flawed. However, analternative conclusion is that 2,800 p.s.i. is the minimum acceptabletensile strength and that the 2,700 p.s.i. tensile is too low. However,the minimum tensile should be 2,800 p.s.i. or higher.

The minimum viscosity that will hold in the remainder portion is 90 to100 c.p.s. But this viscosity resin results in deterioration.

At 200 c.p.s. viscosity the resin held in the four season climate and inSouthern California, and is satisfactory in deterioration performanceshowing only very slight deterioration over time. Thus 200 c.p.s. is theminimum satisfactory viscosity for all fault conditions.

At 300 c.p.s. even the slight deterioration was gone and therefore 300c.p.s. is considered the optimum low end of the range for the remainderportion of a repair for all fault conditions.

In another test resins of 1,500 and 1,200, 1,000 and 800 c.p.s. wereused in an outside repair when the ambient temperature and thewindshield were substantially below room temperature. In this case the1,500 c.p.s. and the 1,200 c.p.s. samples failed quickly but the 800c.p.s and 1,000 c.p.s. sample did not fail and did not deteriorate.Therefore when working in an environment below room temperature theresin viscosity should be 1,000 c.p.s. but not lower than 100 c.p.s.Resins higher than 1,000 c.p.s. when cold will not flow into the pitsand crevices and the bond will be compromised. A premise of the tests isthat a four season climate presents the most problematical circumstanceand that failure or deterioration in Southern California implies thatfailure or deterioration would occur in a four season climate. But,non-failure in Southern California is not indicative of the failurepotential in a four season climate. Deterioration observations inSouthern California and in a four season climate were consistent.

Room Temperature is a commonly used reference understood to mean thattemperature at which a room will be comfortable for human occupation. Atemperature between 68° F. and about 76° F. is generally the rangeconsidered to be room temperature. By contrast, in the present contextreferences to environment below room temperature means about 65° F. andlower although a lower limit of this range is suggested by a limit ofhuman comfort and adverse effects on the resin. While these are notprecise definitions it is important to distinguish the line below roomtemperature as substantially affecting the viscosity of a resin, suchthat the manufacturer's specified viscosity as at room temperature is nolonger applicable and the viscosity increases to the extent that thecrack is not properly filled.

The business of windshield repair must be also considered. This businessis operated by entrepreneurs or others whose training and skill is oftenmodest. The repair technician typically buys tools and resins from awindshield repair supplier such as Ultra-Bond Inc. of Riverside Calif.The resins are not supplied in fine gradations of viscosity, rather atypical set of resins may contain 4-8 different resins. Also, to besuccessful, a technician must be able to do repairs outside at thecustomer's location. Temperatures lower than room temperature havegreater impact on the potential for problems than do temperatures at orhigher than room temperature. In other words operations in a four seasonclimate present the greatest potential for problems, both because of theproblems presented during the repair and the impact of wide temperaturevariations after the repair is made.

The conclusion is that the all season range of viscosities for use inthe remainder portion of a crack is above about 100 c.p.s. and belowabout 1,000 c.p.s.

When limited to use at room ambient temperature, the upper rangelimitation can be ignored and resins above 1,000 c.p.s. can be used.Resins up to 20,000 c.p.s. have been successfully used. As noted above,under these conditions, the general rule of highest viscosity possibleis applicable as long as it flows and completely fills the crack and itspits and crevices.

But, when operating in a substantially lower than room ambienttemperatures environment, the 1,000 c.p.s. viscosity and lower should beobserved.

It should be appreciated that reference to choice of resin viscosityrefers to viscosity specified by the manufacturer which is understood tobe measured at room temperature. A colder ambient temperature willeffect the viscosity, raising it, while a warmer ambient temperaturewill lower the viscosity. A good rule of thumb is that viscosity willreduce by about 1/2 at about 100° F.-110° F. and it should not be heatedmore than about 115° F.

Another variable in methodology is heating the windshield, injectorand/or the resins when the ambient temperature is cold. This willenhance flow by reducing the viscosity of the resin temporarily therebyensuring good crack filling and good adhesion. Enhancing flow is notalways desirable, a thick resin not only works better in a wide crack,but fills the crack better than a thin resin. If it is made too thin, itmay not fill or stay in the crack prior to curing. Thus the resin flowcharacteristics should be such that it can be readily inserted into thecrack, will flow into tiny pits and crevices and will stay in placeuntil cured. As noted herein, beyond those flow characteristics, theresistance to deterioration and failure also enter into the choice ofresin.

For case of repair a minimum of two resins is preferred. For example a1,000 c.p.s. resin at the edge and through the entire remainder portionand a 40 c.p.s. resin in the point portion. On a crack with widevariations in width three resins could be used, for example a 4,000c.p.s. resin in the edge portion, a 300 c.p.s. resin in the intermediateportion and a 40 c.p.s. resin in the point portion. Theoretically, manygradations could be used, but as pointed out above practicalconsiderations, skill of the technician, time, type of tool used, andthe temperature of the environment in which the repair is conducted urgelimiting the number of resins in a particular crack. It is consideredthat a resin which is not successful in Southern California will not besuccessful in a four season climate. On the other hand the four seasonclimate presents the greatest challenge.

What is claimed is:
 1. A method of repairing a crack in a windshieldhaving two layers of glass and a plastic layer between the two glasslayers and each glass layer having a periphery defining a glass areahaving an outer surface within the periphery and having at least oneedge joining the glass area at the periphery, the crack being in onelayer and being over six inches in length and having a first end withinthe glass area and a second end either within the glass area or at theedge of the glass and having a length of the crack which is surfaced oropen defining a reminder portion and a length of the crack which isunsurfaced or tight defining an effectively unsurfaced portioncomprising;inserting a first resin having a preselected viscosity intothe effectively unsurfaced portion of the crack; inserting a secondresin having a viscosity which is higher than that of the first resin,into the remainder portion of the crack by progressively injecting saidsecond resin along the surfaced length of the crack; and causing theresin to cure; wherein the first resin has a viscosity up to about 100c.p.s. and the second resin has a viscosity at least about 150 c.p.s. 2.The method of claim 1 wherein the second resin has a viscosity of atleast about 200 c.p.s.
 3. The method of claim 2 wherein the remainderportion of the crack extends to the edge of the glass area.
 4. Themethod of claim 1 wherein the remainder portion of the crack extends tothe edge of the glass area.